Multi-rotor planetary rotor machines may be utilized as positive displacement devices in a variety of applications. A planetary rotor machine typically employs 3 or 4 rotors equally disposed around a central machine axis. All of the rotors have the same shape and rotate in the same direction. Together, the multiple rotors cooperative to form an internal working volume, or cavity, bounded by the rotors themselves.
Planetary rotor machines utilize rotors having lobes with an axial helical twist to create an internal “progressive cavity” that conducts fluid along the machine axis in a manner similar to a screw auger. Fluid is introduced at one end of the rotor assembly from a first pressure regime, and is transported by the rotor-formed cavity to the opposite end for discharge into a different pressure regime. In this manner the planetary rotor machine either produces or extracts shaft power.
In a planetary rotor machine, the mutually engaging planetary rotors constitute the radial walls of the progressive cavity, without requiring an external housing. Axial walls of the cavity are provided by flat, stationary head plates, or “manifolds”, that abut opposite ends of the rotor assembly. In this manner, and unlike conventional twin screw machines, planetary rotor machines do not require a precision encasement surrounding the rotor assembly. Rather, the cavities are formed by the meshing rotors in cooperation with the flat manifolds abutting the rotor ends.
The general concept of using planetary rotor machines for positive displacement applications has been proposed; however, in practice certain challenges have prevented the commercial adoption of such machines. For example, with some rudimentary manifold configurations, such as a single circular fluid entry opening or port, at certain angular orientations of the rotors pressurized fluid at the manifold-rotor junction may bypass the cavity entirely and flow freely around the outside of the rotors. Such escaping fluid may significantly comprise the efficiency of the planetary rotor machine, and thereby constrain or eliminate the functional and/or commercial viability of such machines. Conversely, sizing a fluid entry port at the manifold-rotor junction too conservatively creates an internal pressure drop and loss of operating efficiency.
One prior attempt to address the problem of manifold-rotor fluid traversal is found in U.S. Pat. No. 3,234,888, which discloses a four-rotor rotary pump enclosed in a rotor casing. A complex valving arrangement utilizes separate rotatable valve “plates” that are mounted on each rotor shaft. Each rotatable valve plate mates with a corresponding stationary portal to channel fluid into the cavity at the correct rotor angular orientation. Such a configuration, however, is ill-suited for a planetary rotor machine that does not utilize an external housing, and further introduces manufacturing and design complexities as well as moving parts that require precision tolerances.